{"id":{"repo_id":"gatech","oai_identifier":"oai:repository.gatech.edu:1853/10479"},"canonical_url":"https://search.dev.ndltd.org/etd/gatech/oai:repository.gatech.edu:1853/10479","repository":{"repo_id":"gatech","name":"Georgia Tech","base_url":"https://repository.gatech.edu/server/oai/request"},"display":{"title":"Multiscale Modeling of the Deformation of Semi-Crystalline Polymers","abstract":"The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation.","abstract_html":"The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation.","abstract_has_math":false,"creators":["Shepherd, James Ellison"],"institution":"Georgia Institute of Technology","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":"Mechanical Engineering","school":null,"contributors":[],"advisors":["McDowell, David L.","Jacob, Karl I."],"committee_chairs":[],"committee_members":["Qu, Jianmin","Tannenbaum, Rina","Zhou, Min"],"year":2006,"date_issued":"2006-03-29","date_published":"2006-03-29","updated_at":"2026-07-27T19:49:46Z","subjects":["Entanglements","Molecular dynamics","Constitutive model","Crystal","Internal state variable","Polymers"],"languages":["en_US"],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/1853/10479","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["McDowell, David L.","Jacob, Karl I."]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Qu, Jianmin","Tannenbaum, Rina","Zhou, Min"]},{"key":"dc:contributor.department","label":"Department","values":["Mechanical Engineering"]},{"key":"dc:creator","label":"Author","values":["Shepherd, James Ellison"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2006-06-09T18:08:13Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2006-06-09T18:08:13Z"]},{"key":"dc:date.issued","label":"Date","values":["2006-03-29"]},{"key":"dc:publisher","label":"Institution","values":["Georgia Institute of Technology"]},{"key":"dc:type","label":"Dc Type","values":["Text"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Entanglements","Molecular dynamics","Constitutive model","Crystal","Internal state variable","Polymers"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["en_US"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/1853/10479"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph.D."]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Multiscale Modeling of the Deformation of Semi-Crystalline Polymers"]}]}],"canonical_facts":{"dc:contributor.advisor":["McDowell, David L.","Jacob, Karl I."],"dc:contributor.committeemember":["Qu, Jianmin","Tannenbaum, Rina","Zhou, Min"],"dc:contributor.department":["Mechanical Engineering"],"dc:creator":["Shepherd, James Ellison"],"dc:date.accessioned":["2006-06-09T18:08:13Z"],"dc:date.available":["2006-06-09T18:08:13Z"],"dc:date.issued":["2006-03-29"],"dc:description.abstract":["The mechanical and physical properties of polymers are determined primarily by the underlying nano-scale structures and characteristics such as entanglements, crystallites, and molecular orientation. These structures evolve in complex manners during the processing of polymers into useful articles. Limitations of available and foreseeable computational capabilities prevent the direct determination of macroscopic properties directly from atomistic computations. As a result, computational tools and methods to bridge the length and time scale gaps between atomistic and continuum models are required. In this research, an internal state variable continuum model has been developed whose internal state variables (ISVs) and evolution equations are related to the nano-scale structures. Specifically, the ISVs represent entanglement number density, crystal number density, percent crystallinity, and crystalline and amorphous orientation distributions. Atomistic models and methods have been developed to investigate these structures, particularly the evolution of entanglements during thermo-mechanical deformations. A new method has been created to generate atomistic initial conformations of the polymer systems to be studied. The use of the hyperdynamics method to accelerate molecular dynamics simulations was found to not be able to investigate processes orders of magnitude slower that are typically measurable with traditional molecular dynamics simulations of polymer systems. Molecular dynamics simulations were performed on these polymer systems to determine the evolution of entanglements during uniaxial deformation at various strain rates, temperatures, and molecular weights. Two methods were evaluated. In the first method, the forces between bonded atoms along the backbone are used to qualitatively determine entanglement density. The second method utilizes rubber elasticity theory to quantitatively determine entanglement evolution. The results of the second method are used to gain a clearer understanding of the mechanisms involved to enhance the physical basis of the evolution equations in the continuum model and to derive the models material parameters. The end result is a continuum model that incorporates the atomistic structure and behavior of the polymer and accurately represents experimental evidence of mechanical behavior and the evolution of crystallinity and orientation."],"dc:description.degree":["Ph.D."],"dc:format.mimetype":["application/pdf"],"dc:identifier.uri":["http://hdl.handle.net/1853/10479"],"dc:language.iso":["en_US"],"dc:publisher":["Georgia Institute of Technology"],"dc:subject":["Entanglements","Molecular dynamics","Constitutive model","Crystal","Internal state variable","Polymers"],"dc:title":["Multiscale Modeling of the Deformation of Semi-Crystalline Polymers"],"dc:type":["Text"]},"updated_at":"2026-07-27T19:49:46Z"}